1. Field of the Invention
The present invention relates to a structure of a gas vent hole formed in a rotor of a synchronous induction electric motor which is started by mainly utilizing induction torque and in which a synchronous operation is performed by utilizing reluctance torque. The synchronous induction electric motor is used for a sealed type compressor etc.
2. Description of Related Art
As described in the document such as Utility Model Gazette No. 64-36581, a gas vent hole is provided in a rotor of an electric motor used for a sealed type compressor in order to enhance the efficiency of the sealed type compressor and reduce a pressure loss by way of making refrigerant gas pass better. In this case, the type of the electric motor is an induction electric motor, or a brushless DC motor in which a permanent magnet is used for the rotor.
Also, as described in Utility Model Gazette No. 64-36581, an oil shielding board is provided at the exit of the gas vent hole of the rotor so that lubricating oil in the sealed type compressor, which is mixed with refrigerant gas and tends to circulate into a refrigerant circuit, may be lessened. This aims at reducing oil lack in the sealed type compressor and enhancing the efficiency of the refrigerating cycle.
As mentioned above, it is necessary to provide a gas vent hole which makes refrigerant gas pass, in the rotor of the electric motor used for a sealed type compressor. It is also necessary to provide a gas vent hole when a synchronous induction electric motor where a rotor slit to generate reluctance torque is filled up with aluminum and both ends of the rotor are short-circuited by end-rings is used for a sealed type compressor. However, since the slit formed in the rotor is filled up with aluminum, it is difficult to provide a hole in the slit part. Furthermore, since the portion without the slit is a place where magnetic bundle passes, if a hole is shaped in such a portion, there will be a problem of increasing magnetic resistance to cause an output fall and efficiency decrease.